Flexible optical circuits are utilized in a wide variety of applications in which fiber management is desirable. For example, flexible optical circuits are commonly utilized as optical back planes to interconnect a number of printed circuit boards or the like. Similarly, flexible optical circuits can serve as ribbons of optical fibers in order to route the optical fibers in an organized fashion.
Regardless of the application, a flexible optical circuit is commonly formed of a plastic substrate, typically formed of a polyimide or similar types of engineering thermoplastic materials, such as polyetherimide or polybutylene terphthalate. Most commonly, however, the substrate is formed of Kapton™ polyimide. The substrate is coated with an adhesive, such as a silicone adhesive, and a plurality of optical fibers are placed upon the adhesive-coated substrate. In particular, the optical fibers are placed in a predetermined pattern upon the substrate in order to appropriately route the optical fibers. The flexible optical circuit is then completed by placing another layer over the optical fibers. For example, a flexible optical circuit can include another layer of the plastic material that forms a substrate in order to effectively sandwich the optical fibers between the layers of plastic. By way of example, the flexible optical circuit can include a layer formed of Kapton™ polyimide that overlies the optical fibers and is adhered to the substrate. Alternatively, a conformal coating can be applied so as to cover the substrate and the optical fibers adhered to the substrate. For example, a conformal coating of silicone can be sprayed on the substrate in order to cover the optical fibers as well as other portions of the substrate.
The optical fibers of a flexible optical circuit generally extend from a first end proximate one edge of the substrate, across the substrate to an opposed second end proximate another edge of the substrate. In one common application, flexible optical circuits are utilized to create and route ribbons of optical fibers. As such, the optical fibers are arranged in groups, at least in those regions proximate the edges of the substrate at which the optical fibers enter and exit the optical circuit. Each group of optical fibers may form a respective ribbon with the substrate serving as the matrix material to bind the optical fibers together. Depending upon the desired fiber count of a ribbon, the groups of optical fibers may have four, six, eight, twelve, sixteen or any other number of optical fibers. While the optical fibers may cross one another and follow various curved paths across a medial portion of the substrate to permit the optical fibers to be grouped differently proximate the different edges of the substrate, each group of optical fibers generally extends parallel to and is spaced from the other groups of optical fibers proximate an edge of the substrate. The relatively empty portions of the optical circuit between the groups of optical fibers proximate the edge of the substrate may then be removed to permit more independent movement of each ribbon of optical fibers. Generally, a respective fiber optic connector is also mounted upon the end portions of the optical fibers of each group.
Fiber optic connectors designed to mount upon and interconnect a greater number of optical fibers, typically arranged in the form of multiple ribbons, have been developed and are desirable for certain applications. Typically, these fiber optic connectors are designed to be mounted upon the end portions of a plurality of ribbons of optical fibers with the ribbons of optical fibers disposed in a stacked configuration so that one ribbon overlies another. As such, the fiber optic connector can permit the interconnection of a plurality of optical fibers arranged in a relatively dense manner.
In order to mount a fiber optic connector upon the end portions of a plurality of ribbons of optical fibers that extend outwardly from the main portion of a flexible optical circuit, the ribbons of optical fibers are moved into alignment with one another in a stacked configuration. As such, most, if not all, of the ribbons of optical fibers are bent somewhat in order to move the ribbons into alignment and to stack the ribbons in a multi-layered fashion that will be compatible with a typical fiber optic connector designed to receive a two-dimensional array of optical fibers. When bending the ribbons of optical fibers, stress is created on the optical fibers. As known to those skilled in the art, stress is disadvantageous for optical fibers and may introduce attenuation and have other deleterious performance effects.
In an attempt to reduce the stress to which the optical fibers are subjected, the ribbons of optical fibers have been made longer. While the lengthening of the ribbons of optical fibers reduces, to some extent, the stress to which the optical fibers are subjected, the increased length of the ribbons of optical fibers is oftentimes disadvantageous for fiber management and organization purposes. Moreover, while the stress to which the optical fibers is subjected may be reduced somewhat by increases in the length of the ribbons of optical fibers, the optical fibers will still be subjected to at least some stress which, in turn, degrades the performance of the flexible optical circuit.
It would therefore be desirable to provide an improved flexible optical circuit having a plurality of ribbons of optical fibers that may be more readily arranged in a stacked configuration for insertion into a fiber optic connector. In this regard, it would be desirable for the flexible optical circuit to be designed such that the ribbons of optical fibers may be arranged in a stacked configuration with only a minimal, if any, amount of stress placed upon the optical fibers as the optical fibers are arranged in the stacked configuration.